1. Field of the Invention
The present invention relates to an image forming apparatus, which has a plurality of image forming stations for forming an image corresponding to different colors, respectively, on an image bearing member, and transfers the image formed at each image forming station on a transferring material transported by a transporting member to form an image, or an image forming apparatus for sequentially transferring an image formed at each image forming station on an intermediate transfer member and then transferring the image on a transferring material, and a registration correcting method of the image forming apparatus.
2. Related Background Art
Conventionally, an image forming apparatus has been proposed which has a plurality of image forming portions for irradiating a laser beam that is optically modulated according to recording information on a photosensitive drum, developing an electrostatic latent image of a drum by an electrophotographic process and transferring an image on a transferring material, and is capable of multiply transferring each color image on a transferring material while sequentially transporting the transferring material to each image forming portion by a transfer belt to form a color image. In addition, an image forming apparatus is also proposed which sequentially superimposes images, which are formed by a plurality of image forming portions, to form the images on an intermediate transfer member and then collectively transfers the images on a transferring material.
In a case of using an image forming apparatus of this type, a phenomenon in which registration of each color image does not match due to a mechanical attachment error of each photosensitive drum, an error of an optical length of each laser beam, a change in an optical path, or the like when an electrostatic latent image is formed on each photosensitive drum, and the electrostatic latent image is developed and transferred on a transferring material on a transfer belt. Thus, conventionally, a pattern image for registration correction formed on a transfer belt is read by a CCD sensor or the like from each photosensitive drum, misregister is detected on a photosensitive drum corresponding to each color, an image signal that should be recorded is electrically corrected, or a reflection mirror provided in an optical path of a laser beam is driven to change an optical length or to correct a change in an optical length.
However, when registration (misregister) correction is executed in an image forming apparatus of this type, a difference of a level of reading a registration correction pattern is caused due to a difference of an image forming density of the registration correction pattern (a mark for detecting a misregister) to be recorded by each recording apparatus, that is, a difference of a colorant to be developed and transferred or the like. Therefore, a difference of a level of detecting the registration correction pattern is caused. In general, it is known that toner of magenta (Ma), cyan (Cy), yellow (Ye) and black (Bk) has a magnitude of reflectance of infrared ray in the order of Ma greater than Cy greater than Ye greater than Bk by an influence of their colorant components. A difference of a detection level due to a difference of reflectance of each colorant will be described with reference to FIGS. 18A, 18B, 18C and 18D.
FIGS. 18A to 18D are views showing an example of an output characteristic for reading a registration correction pattern in an image forming apparatus of this type. An upper section of each view in FIGS. 18A to 18D shows a registration correction pattern in a cross shape in each colorant of Ma, Cy, Ye and Bk as an example of a registration correction pattern. A lower section of each view in FIGS. 18A to 18D shows a waveform of the registration correction pattern read by a CCD sensor and converted into a histogram by accumulating the read data in a sub-scanning direction.
As shown in FIGS. 18A to 18D, when reading of a registration correction pattern is executed, a histogram of each colorant shows a waveform having a different peak value and slope of the line.
A difference between each colorant cannot be determined unconditionally because it affects colorant components, optical length or the like. However, a difference of a level of detecting each registration correction pattern is caused due to the difference, and a colorant with a low detection level has a worse detection accuracy of a registration correction pattern compared with a colorant with a high detection level.
As a result, there is a problem in that it is difficult to perform an adjustment of high accuracy when an image signal that should be recorded is electrically corrected, and/or an optical length is changed or a change in an optical length is corrected by driving a reflecting mirror provided in an optical path of a laser beam according to a misregistration amount obtained by detecting a registration correction mark recorded by each image forming portion.
The present invention has been made in view of the above problems, and it is an object of the present invention to provide an image forming apparatus and a registration correction method of the image forming apparatus with which a detection level can be maintained constant to perform registration correction of high accuracy regardless of a color of a registration correction mark.
In order to attain the above-mentioned object, the present invention provides an image forming apparatus which includes a plurality of image forming means for forming images with different colors, respectively transporting means for bearing and transporting a transferring material, transferring means for sequentially transferring an image formed by each of image forming means, to the transferring material,
mark forming means for controlling each of the image forming means in order to form a misregister detection mark and controlling the transferring means in order to transfer the misregister detection mark to the transporting means;
illuminating means for illuminating the misregister detection mark on the transporting means;
reading means for reading the misregister detection mark illuminated by the illuminating means;
correcting means for corrected misregister based on information from the reading means; and
adjusting means for adjusting a light amount of the illuminating means based on colors of a plurality of misregister detection marks.
In another aspect of the present invention, an image forming apparatus includes a plurality of image forming means for forming images with different colors, respectively, and transferring means for sequentially transferring an image formed by each of image forming means, to an intermediate transfer member, wherein the image forming apparatus includes:
mark forming means for controlling each of the image forming means in order to form a misregister detection mark;
illuminating means for illuminating the misregister detection mark on the intermediate transfer member;
reading means for reading the misregister detection mark illuminated by the illuminating means;
correcting means for correcting a misregister based on information from the reading means; and
adjusting means for adjusting a light amount of the illuminating means based on colors of a plurality of misregister detection marks to be read.
Moreover, in another aspect, of the present invention is directed to a method of correcting a misregister among a plurality of image forming means in an image forming apparatus sequentially superimposing images formed by the plurality of image forming means to form an image, wherein the method includes:
a mark forming step for controlling the plurality of image forming means in order to form a misregister detection mark;
an illuminating step for illuminating the misregister detection mark formed by each of the plurality of image forming means;
a reading step for reading the misregister detection mark illuminated by the illuminating step;
a correcting step for correcting a misregister based on information obtained in the reading step; and
an adjusting step for adjusting a light amount of the illuminating means based on colors of a plurality of misregister detection marks to be read.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.